PROJECT SUMMARY The impairment in the clearance of amyloid-b (Ab) is increasingly recognized as one of the critical mechanism of Ab deposition in Alzheimer's disease (AD). A substantial portion of Ab clearance is mediated by the glymphatic system, which is a brain-wide pathway for fluid transport consisting of the para-artetial influx of cerebrospinal fluid, bulk flow of interstitial fluid through extracellular space (ECS), and the clearance along the draining vein. Hyaluronan (HA), a large anionic polysaccharide belonging to the family of glycosaminoglycans, is a major constituent of the extracellular matrix of the adult brain. Because of its extremely hydrophilic nature, HA has an extremely large hydrodynamic volume and exerts profound effects on the volume, water content, and pressure of the interstitial space in various tissues. Consistently, our previous study demonstrated that HA modulates the volume of brain ECS and fluid movement through it. Since the volume of ECS is considered to be one of the determinants of glymphatic function, these findings led us to hypothesize that HA is functionally involved in the clearance of brain waste products, such as Ab. As an initial test for the hypothesis, we recently examined whether Ab accumulation is accelerated in compound mutant mice in which one of the hyaluronan synthase genes (Has3) is deleted in the APP/PS1 AD mouse model. We found that these compound mutants indeed exhibit enhanced Ab accumulation and amyloid plaque formation. Based on these observations, we propose a project to determine the role of HA in the glymphatic system and the pathogenesis of AD. Specific aims are: 1. Determine the role of HA in glymphatic fluid transport. 2. Determine the role of HA in the clearance and deposition of Ab. 3. Investigate whether enhancing HA production by virus-mediated gene transfer ameliorates pathological and cognitive deficits in APP/PS1 mice. Addressing these questions will shed new light to the regulatory mechanism of the glymphatic system and could provide a novel insight into potential therapeutic approach for AD.